1. Field of the Invention
This invention relates to power supplies and, more particularly, to the protection of microprocessor power supplies.
2. Description of the Related Art
Power supplies are used in various types of devices. There are many specialized types of power supply circuits with various advantages and disadvantages. Microprocessors in computers may require a power supply circuit that regulates a high level of current while maintaining a high level of efficiency.
One such type of specialized power supply circuit is a switching regulator. Switching regulator circuits typically provide a lower voltage output than the unregulated input while at the same time providing a higher current than the current drawn from the unregulated supply. This is accomplished using a transistor that is constantly switching between a saturation mode and a non-conducting mode. Typically a transistor that is optimized for power applications, such as a power field effect transistor, is used. Because the transistor is either in saturation or not conducting, there is very low power dissipation. A switching regulator therefore can regulate a high amount of current at a high efficiency rate.
Since these power supply circuits regulate a high level of current during normal operation, they may also generate a significant amount of heat while operating. Under normal operating conditions the heat may not cause problems. However, under less than ideal conditions such as, for example, short circuits, improper power supply operation and unacceptable environmental conditions, the heat may become excessive. Excessive heat may cause damage to various computer system components including the motherboard, the microprocessor, or the power supply itself.
The heat generated by the switching regulator may be controlled by methods such as directed airflow and the use of heat sinks. These methods may be effective in some cases, but in order to accommodate the worst case operating conditions, those methods may be expensive. Additionally, it may be impossible to anticipate the worst possible conditions.
Various embodiments of a power supply circuit including a thermal protection circuit are disclosed. In one embodiment, the power supply circuit includes a switching control circuit coupled to a switching regulator circuit. The switching control circuit is configured to generate a plurality of switching control signals for controlling the switching regulator circuit. The power supply circuit also includes a temperature sensitive circuit including a thermistor. The temperature sensitive circuit is configured to provide a variable voltage level output to the phase control circuit. The switching control circuit is also configured to suspend operation of the switching regulator circuit upon detecting a predetermined voltage level at the output.
In another embodiment, the power supply circuit includes a phase control circuit coupled to a first switching regulator circuit and to a second switching regulator circuit. The phase control circuit is configured to generate a plurality of switching control signals for controlling switching of the first and second switching regulator circuits. The phase control circuit is also configured to selectively suspend operation of the second switching regulator circuit in response to receiving a signal indicative of a low power mode of operation. The power supply circuit also includes a temperature sensitive circuit which includes a thermistor. The temperature sensitive circuit is configured to provide a variable voltage level output to the phase control circuit. The phase control circuit is further configured to suspend operation of the first and second switching regulator circuits upon detecting a predetermined voltage level at the output.
In various other embodiments, the thermistor is configured to detect an elevation in temperature of the first switching regulator circuit or the second switching regulator circuit and to change a resistance value internal to the thermistor. Furthermore, the thermistor is configured to decrease the internal resistance value in response to detecting the elevation in temperature. The temperature sensitive circuit develops the predetermined voltage level in response to the thermistor decreasing the internal resistance value.